From: "Michael S. Tsirkin" <mst@redhat.com>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Michael Bommarito <michael.bommarito@gmail.com>,
Olivia Mackall <olivia@selenic.com>,
linux-crypto@vger.kernel.org, Jason Wang <jasowang@redhat.com>,
Kees Cook <kees@kernel.org>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
virtualization@lists.linux.dev, linux-kernel@vger.kernel.org,
Dan Williams <djbw@kernel.org>, Ingo Molnar <mingo@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
torvalds@linux-foundation.org, alan@linux.intel.com,
tglx@linutronix.de
Subject: Re: [PATCH v3] hwrng: virtio: clamp device-reported used.len at copy_data()
Date: Thu, 11 Jun 2026 03:30:14 -0400 [thread overview]
Message-ID: <20260611025916-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <aio83ZWadVTiuNpR@gondor.apana.org.au>
On Thu, Jun 11, 2026 at 12:43:09PM +0800, Herbert Xu wrote:
> On Sun, May 31, 2026 at 10:22:51AM -0400, Michael Bommarito wrote:
> >
> > + size = min_t(unsigned int, size, avail - vi->data_idx);
> > + idx = array_index_nospec(vi->data_idx, sizeof(vi->data));
> > + memcpy(buf, vi->data + idx, size);
>
> I don't see how nospec can help here. Please enlighten me.
All the "malicious device" things are confusing. Spectre things -
doubly so.
So if an access is speculated then CPU might speculate feeding a kernel
secret into RNG. And then the speculated RNG value maybe can be also
speculatively be used by some kernel code as an index
to trigger a cache access, finally leaking the secret?
Maybe?
> Thanks,
> --
> Email: Herbert Xu <herbert@gondor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
next prev parent reply other threads:[~2026-06-11 7:30 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-31 14:22 [PATCH v3] hwrng: virtio: clamp device-reported used.len at copy_data() Michael Bommarito
2026-06-11 4:43 ` Herbert Xu
2026-06-11 7:30 ` Michael S. Tsirkin [this message]
2026-06-11 7:46 ` Herbert Xu
2026-06-11 7:58 ` Michael S. Tsirkin
2026-06-11 8:18 ` Herbert Xu
2026-06-11 9:10 ` Michael S. Tsirkin
2026-06-11 9:19 ` Herbert Xu
2026-06-11 10:42 ` Michael S. Tsirkin
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